1. Field of the Invention
The present invention relates to a magnetoresistive film using a perpendicular magnetic anisotropy film that can reverse its magnetization by a relatively small applied magnetic field and shows a relatively large magnetoresistive effect, and to a memory using the magnetoresistive film.
2. Related Background Art
The basic structure of a magnetoresistive film is a sandwiched structure formed by putting a non-magnetic layer between magnetic layers adjoining to each other. Cu and Al2O3 can be cited as materials used as the non-magnetic layer frequently. A magnetoresistive film using a conductor such as Cu as its non-magnetic layer is called as a giant magnetoresistive film (GMR film). And, a magnetoresistive film using an insulator such as Al2O3 is called as a spin dependent tunneling magnetoresistive film (TMR film). Generally, a TMR film shows a larger magnetoresistive effect than that of a GMR film. Various applications of such a magnetoresistive film can be considered.
A memory using the magnetoresistive effect (MRAM) has recently been considered to be promising particularly among them. The MRAM is promising as a memory satisfying all specifications required by many kinds of information equipment in the aspects of its recording time, its reading time, its recording density, its possible number of times of rewriting, its electric power consumption and the like. In particular, because a large readout signal can be obtained from an MRAM using the spin dependent tunneling magnetoresistance (TMR) effect, the MRAM is advantageous to the increase of a recording density or to high speed readout. The realizability of the MRAM has been verified by recent reports of researches.
If the magnetization directions of two magnetic layers 13 and 14 are parallel to each other as shown in FIG. 11A, the electric resistance of the magnetoresistive film is relatively small. If the magnetization directions of the two magnetic layers 13 and 14 are anti-parallel to each other as shown in FIG. 11B, the electric resistance of the magnetoresistive film is relatively large. Consequently, it is possible to read information from the magnetoresistive film by utilizing the above-mentioned property by using one of the magnetic layers 13 and 14 as a memory layer and the other of them as a detection layer. For example, a magnetic layer 13 located above a non-magnetic layer 12 is used as the memory layer; a magnetic layer 14 located under the non-magnetic layer 12 is used as the detection layer; the state in which the magnetization direction of the memory layer faces to the right is supposed to the state of record information xe2x80x9c1xe2x80x9d; and the state in which the magnetization direction of the memory layer faces to the left is supposed to the state of record information xe2x80x9c0xe2x80x9d. If the magnetization directions of both of the magnetic layers 13 and 14 face to the right as shown in FIG. 12A, the electric resistance of the magnetoresistive film is relatively small. If the magnetization direction of the detection layer faces to the right and the magnetization direction of the memory layer faces to the left as shown in FIG. 12B, the electric resistance of the magnetoresistive film is relatively large. Moreover, if the magnetization direction of the detection layer faces to the left and the magnetization direction of the memory layer faces to the right as shown in FIG. 12C, the electric resistance of the magnetoresistive film is relatively large. If the magnetization directions of both of the magnetic layers 13 and 14 face to the left as shown in FIG. 12D, the electric resistance of the magnetoresistive film is relatively small. That is, if the magnetization direction of the detection layer is fixed to face. to the right, the record information xe2x80x9c0xe2x80x9d is recorded in the memory layer when the electric resistance is large, and the record information xe2x80x9c1xe2x80x9d is recorded in the memory layer when the electric resistance is small. Or, if the magnetization direction of the detection layer is fixed to face to the left, the record information xe2x80x9c1xe2x80x9d is recorded in the memory layer when the electric resistance is large, and the record information xe2x80x9c0xe2x80x9d is recorded in the memory layer when the electric resistance is small.
If the device size of the MRAM is made to be smaller for increasing the recording density thereof, the problem is produced in which it becomes impossible for the MRAM using an in-plane magnetic film to hold information owing to the influences of a demagnetization field or the curling of magnetization on end faces. For escaping the problem, a measure such as forming the shapes of the magnetic layers to be a rectangle can be cited. However, the measure cannot make the size of the device smaller, and consequently it is difficult to expect the improvement of the recording density. Accordingly, the proposal of escaping the above-mentioned problem by the use of a perpendicular magnetic anisotropy film was submitted, for example, as the disclosure in U.S. Pat. No. 6,219,725. Because the demagnetizing field does not increase even if the device size becomes small in accordance with the method, the method makes it possible to realize a magnetoresistive film having a size smaller than that of the MRAM using the in-plane magnetic film.
Like the magnetoresistive film using the in-plane magnetic film, the electric resistance of the magnetoresistive film using the perpendicular magnetic anisotropy film is relatively small if the magnetization directions of two magnetic layers are parallel to each other, and the electric resistance becomes relatively large if the magnetization directions are anti-parallel to each other. In FIGS. 13A, 13B, 13C and 13D, a magnetic layer 23 located above a non-magnetic layer 22 is used as a memory layer; a magnetic layer 21 located under the non-magnetic layer 22 is used as a detection layer; the state in which the magnetization direction of the memory layer faces upward is supposed to the state of the record information xe2x80x9c1xe2x80x9d; and the state in which the magnetization direction of the memory layer faces downward is supposed to the state of the record information xe2x80x9c0xe2x80x9d. If the magnetization directions of both of the magnetic layers 23 and 21 face upward as shown in FIG. 13A, the electric resistance of the magnetoresistive film is relatively small. If the magnetization direction of the detection layer faces downward and the magnetization direction of the memory layer faces upwards as shown in FIG. 13C, the electric resistance of the magnetoresistive film is relatively large. Moreover, if the magnetization direction of the detection layer faces upward and the magnetization direction of the memory layer faces downward as shown in FIG. 13B, the electric resistance of the magnetoresistive film is relatively large. And, if the magnetization directions of both of the magnetic layers 23 and 21 face to downward as shown in FIG. 13D, the electric resistance of the magnetoresistive film is relatively small. That is, if the magnetization direction of the detection layer is fixed to face upward, the record information xe2x80x9c0xe2x80x9d is recorded in the memory layer when the electric resistance is large, and the record information xe2x80x9c1xe2x80x9d is recorded in the memory layer when the electric resistance is small. Or, if the magnetization direction of the detection layer is fixed to face downward, the record information xe2x80x9c1xe2x80x9d is recorded in the memory layer when the electric resistance is large, and the record information xe2x80x9c0xe2x80x9d is recorded in the memory layer when the electric resistance is small.
The following films can be cited chiefly as the perpendicular magnetic anisotropy film: an alloy film or an artificial lattice film which is composed of at least one kind of element selected among rare earth metals such as Gd, Dy and Tb and at least one kind of element selected among transition metals such as Co, Fe and Ni, an artificial lattice film made of a transition metal and a noble metal such as Co/Pt, and an alloy film having a magnetocrystalline anisotropy in the direction perpendicular to film surfaces such as CoCr. Among the materials, the alloy film or the artificial lattice film which is composed of a rare earth metal and a transition metal shows a magnetization curve having a squareness ratio of 1, and then produces a steep magnetization reversal when a magnetic field is applied thereto. Consequently, the alloy film or the artificial lattice film is most suitable to a magnetoresistive film to be used as a memory element.
The magnetic filed at which a magnetization reversal of a perpendicular magnetic anisotropy film is produced is generally larger than that of an in-plane magnetic film composed of a transition metal. For example, although the magnetization reversal magnetic field of Permalloy being an in-plane magnetic film is on the order of several hundreds A/m, the magnetization reversal magnetic field of an artificial lattice film of Co/Pt being a perpendicular magnetic anisotropy film on the order of several tens kA/m, which is remarkably larger. In an alloy film of a rare earth metal and a transition metal, because the sublattice magnetization of the rare earth metal and the sublattice magnetization of the transition metal face in anti-parallel to each other, an apparent intensity of the magnetization of the alloy film changes in compliance with the composition of the film. Consequently, the magnetization reversal magnetic field of the alloy film differs in the composition thereof. A GdFe alloy film has a relatively small magnetization reversal magnetic filed among the alloy films of rare earth metals and transition metals, but the GdFe alloy film has a magnetoresistance ratio on the order of a few percent, which is not a large value.
In the case where a sensor, a memory or the like is constituted by the use of a magnetoresistive film, a large magnetoresistive effect and a small magnetization reversal magnetic field are required for the magnetoresistive film to be used. However, almost no research has been done about a magnetoresistive film using a perpendicular magnetic anisotropy film until now, and no perpendicular magnetic anisotropy film satisfying the above-mentioned requirements has been proposed. Consequently, if perpendicular magnetic anisotropy films having large coercive forces are used, it is necessary to concentrate their stray magnetic fields to the magnetic layers of the magnetoresistive film as, for example, a sensor, and it is necessary to devise a method for generating a large magnetic field as a memory. Although the magnetic field to be applied to a memory is generally generated by flowing an electric current in a lead, in case of a memory to be used in a portable terminal it is not preferable to flow a large electric current owing to the limitation of the capacity of the power supply of the memory. Accordingly, it is required to deal with such a case by, for example, winding a lead for generating a magnetic field around a memory element composed of a magnetoresistive film. However, because such a measure makes the structure and electric circuits around the magnetoresistive film complicated, the manufacturing of such a memory element becomes difficult. And, the measure has the problem of the occurrence of the decrease of a yield rate and the remarkable increase of costs.
In view of the point, the present invention aims to provide a magnetoresistive film using a perpendicular magnetic anisotropy film having the following characteristics and a memory using the magnetoresistive film. That is, the magnetization reversal of the perpendicular magnetic anisotropy film can easily be performed with a small magnetic field, and the perpendicular magnetic anisotropy film shows a comparatively large magnetoresistive effect, and further the film structure of the perpendicular magnetic anisotropy film is simple and the manufacturing thereof is easy.
A magnetoresistive film of the present invention has a structure comprising a non-magnetic film being put between magnetic films, wherein at least one of the magnetic films is a perpendicular magnetic anisotropy film including a rare earth metal, Fe and Co as main ingredients, and composition of Co to Fe and Co is within a range from 8 atomic percent to 97 atomic percent both inclusive.
The magnetoresistive film includes one in which the composition of Co to Fe and Co is within a range from 13 atomic percent to 90 atomic percent both inclusive.
The magnetoresistive film includes one in which the composition of Co to Fe and Co is within a range from 30 atomic percent to 70 atomic percent both inclusive.
The magnetoresistive film includes one in which the magnetic film including a rare earth metal, Fe and Co as the main ingredients is an amorphous alloy.
The magnetoresistive film includes one in which the rare earth metal is at least one element selected from the group consisting of Gd, Dy and Tb.
The magnetoresistive film includes one in which the non-magnetic film is an insulator.
The magnetoresistive film includes one in which the magnetoresistive film shows a spin dependent tunneling magnetoresistance effect when an electric current is made to flow in a direction perpendicular to film surfaces of the magnetoresistive film.
The magnetoresistive film includes one in which a film thickness of the magnetic film laminated on each other with the non-magnetic layer put between them is within a range from 1 nm to 500 nm both inclusive.
The magnetoresistive film includes one in which coercive forces of the two magnetic films laminated with the non-magnetic film put between them differ from each other, and at least one of the magnetic films having a relatively smaller coercive force includes Gd, Fe and Co as main ingredients.
The magnetoresistive film includes one in which coercive forces of the two magnetic films laminated with the non-magnetic film put between them differ from each other, and at least one of the magnetic films having a relatively larger coercive force includes Tb, Fe and Co as main ingredients.
The magnetoresistive film includes one in which the magnetic films are formed by sputtering.
A memory according to the present invention comprises a plurality of magnetoresistive films disposed as memory elements, means for recording information in the magnetoresistive films, and means for reading the information recorded in the magnetoresistive films.
The memory includes one in which the means for recording the information applies a magnetic field having an intensity capable of reversing magnetization of the magnetoresistive films.
The memory includes one in which the magnetic field used as the means for recording the information is generated by making an electric current flow through a lead.
The memory included one in which the means for recording the information includes at least two or more magnetic generation sources applying magnetic fields in different directions to one of the memory elements, and the means for recording performs selective recording by making the plural magnetic fields operate on a selected memory element.
The memory includes one in which one of the two magnetic fields, which is applied in different directions to the memory element to record the information, is directed to a direction which is perpendicular to film surfaces of the memory element to record the information and corresponds to the information to be recorded, and the other magnetic field is applied in an in-plane direction of the memory element to record the information.
The memory includes one in which the magnetic filed being directed in the in-plane direction is generated by an electric current flowing through a bit line disposed above the memory element to record the information.
The details of the present invention will be described in regard to the preferred embodiments of the invention in detail.